Process in the employment of self-baking electrodes



Jan. 31, 1928.

J. WESTLY PROCESS IN THE EMPLOYMENT OF SELF BAKING ELECTRODES Filed "Jag. 5 1925 Patented 31 i UNITED STATES PATENTI- OFFICE;

JENS WESTLY, OF KRISTIANSAND, NORWAY, ASSIGNOR TO DE'I NORSKE: AKTLE- SELSKAB FOR ELEKTBOKEMISK INDUSTRI OF NORWAY, OF OSLO, NORWAY.

rnocnss IN THE EllEPLOYMENT or SELF-BAKING ELECTRODES.

Application filed January 5, 1925, Serial No. 713, and in Norway January 17, I924.

Self-baking electrodes (electrodes which are baked in the furnace in which they are used) provided with metallic mantle are described in United States Patent No.

5 1.440,?24. The mantle has here the func:

tion of acting as a mould during the introduction of the mass, of protecting the electrode against oxidation and, transmitting the currentto the electrode. It isoftendo sirable to provide the electrode with ribs or similar extensions projecting into the electrode mass and further facilitating the flow of the, current. In the use of the electrode the mantle and ribs ordinarily melt in the furnace and the metal contained therein enters into the furnace product.

Usually electrodes contain, according to their size and the current carried,about 4-10% metal, generally iron. 'The amounts of iron' supplied in this way to the furnace are as a rule so small that they do not interfere with the working of the furnace or lower the quality of the product. In some cases it may, however, be of importance to avoid or at least to minimize the introduction of iron, as for instance in using the electrode in furnaces for the production of aluminiumin which about 6-700 kg. of electrodes are consumed per ton of aluminium. This would cause the aluminium to take up about 55-35% iron from the mantle if the electrode contains 5% iron, and thus the quality of the aluminium produced would be greatly lowered. It is therefore of great importance for the employment of the electrode in these furnaces that a method be found to avoid introduction of considerable .quantities of iron or other detrimental metals into the aluminium. This may be accomplished by making the mantle and ribs of aluminium. Iron, however, on account of its high melting point and its cheapness hasimportant advantages as compared with aluminium,-

wherefore if possible iron would preferably be employed. Applicant has found that this reaches far enough down into the furnace so that the mantle melts off. It is then desirable to employ a mantle of the smallest possible thickness; for instance with iron so that the electrode holder is placed on the baked part of the electrode as far as ossible. Whether-this is possible depen s on the temperature favourable circumstances the heatmay, if conditions in the furnace, size of the electrode and the current carried. Under high up in the electrode that it is already sufficiently baked before it enters the holder and the mantle may be removed there. Otherwise the mantle maybe conveniently removed at the lower edge of the electrode holder, for instance in the form of strips 5-10'cm. broad. To facilitate the tearing ofi', arrangements may be made'to give a sharp lower edge to the electrode holder, thus causing it to act as a knife. Further the mantle may be scored horizontally at intervals of 5-10 cm., to facilitate the tearing operation. The tearing operationma preferably be repeated each time the holder is moved.

In the application of the self-baking electrodes herein referred to it is often advantageous to employ ribs. These can, however, only with difliculty be removed by tearing off and as far as the ribs are concerned one has the choice between letting the amount of iron or other detrimental metal corresponding to. the length of the ribs pass into the furnace, or making the ribs of aluminium or other non-detrimental met-.

al or metal alloy. To be able to employ iron in the ribs'the size of the ribs must then in aluminium furnaces be reduced to the minimum. Preferably the holder is as far as possible placed on baked carbon, giving the most direct passage of the current from mantle to the electrode mass below the holder without passing through the ribs. The ribs'may therefore be greatly reduced and in practice it has been possible to reduce the amount of iron in the ribs so much that the aluminium produced only takes up 0.05-0.1% iron from the ribs even if these are allowedto melt down and entirely enter 70 are rightly chosen, be drawn so the aluminium. As an example it may be and electrode.

mentioned that an electrode with 1 meter diameter and for a capacity of 1 ampere per square centimeter was made with 8 ribs 7 centimeters broad. Both ribs and'mantle were of 0.3 mm. plate. The mantle Was during its use removed beforeit entered into k the bath. But the ribs were allowedto' melt I and enter the metal.

took up 0.074% iron.

In the cases when bers of the holder these may. e 'so made as to scale off the metal mantle. p stance as shown in the appended drawing.

.1 is' the electrode, 2.is a part of the holder and 3 shows the mantle which is forced out from the electrode by means of ploughshaped holder parts. The mantle parts which are forced out may be torn or cut away or allowed to burn off.

The metal mantle will always stand out a little from the electrode when this is baked.

produced, which thus T .Musing self-ba the mantle is removed before it gets down into the grigpingmem- For iii-- I claim:

1. In the process of manufacturing'and using self-baking electrodes, where the electrode is-formed and baked Within a protecting metal mantle, the step comprising from time to time removing portions of the mantle from the baked end of the elec-' trode before such portions become melted. 2. Inthe rocess of manufacturing and Eing electrodes, where the electrode is formed and baked within a protecting metal mantle, the step comprising from time to time removing-portions of the mantle from the bakedend of the electrode 7 :in such a manner as to reduce the amount of foreign ,m'etal enteringthei furnace, and at the same time protect-the. electrode dur-- ing the baking period.

3. In .the process ofmanufacturing and using self-baking electrodes, where the electrode is formed and baked within a protecting metal mantle, the step comprising removing a portion of .the amantle above the point'where it would melt and enter the furnace charge.

4, In the process of manufacturingand using self-baking electrodes, where the electrode is formed and baked within a protecting metal mantle, the step comprising removing a portion of the mantle below the electrode holder and above the point where it would melt and enter the furnace-charge.

JENS WESTLY. 

